Build a fault-tolerant Chat Pipeline
Last updated: May 8, 2026
Quick Overview
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ServiceNow
System Design
Software Engineer
ServiceNow
May 8, 2026Software Engineer
System Design Round
System Design
Hard
110
3
4,933 solved
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at ServiceNow typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
Key Topics to Cover
Security and authentication
Requirements gathering and capacity estimation
High-level architecture and component design
Consistency models and replication
Failure handling and fault tolerance
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle schema migrations with zero downtime?
- What monitoring and alerting would you set up on day one?
- How do you ensure data consistency across multiple services?
- How would you handle a region-wide outage?
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Solve on CodemiaSample Answer
Requirements
Functional Requirements
- Real-time Messaging: Users should be able to send and receive messages in real time.
- User Authentication: Users must authenticate securely before accessing th...
Capacity Estimation
Back-of-Envelope Calculation
- User Base: Assume 10 million active users.
- Messages per User: Estimate 100 messages per user per day.
- Total Messages: 10 million users * 100 messa...
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